A kind of high-strength strapping steel and production method thereof

Abstract

The present invention relates to a high-strength strapping steel and a production method thereof. By taking measures in key processes such as steelmaking and continuous casting, hot rolling, laminar cooling, cold rolling, and bluing treatment in sequence, the quality of the core of the substrate is improved, the substrate tissue state is optimized, and the cold rolling and bluing processes are reasonably set, etc., so as to achieve comprehensive regulation of the strength and plasticity of the high-strength strapping steel. The tensile strength R m ≥1000MPa, elongation A 30 ≥12%, which solves the problem of difficulty in producing high-strength and high-elongation strip steel under the conditions of cold rolling combined with bluing process.

Description

Technical Field

[0001] The invention relates to high-strength bundled strip steel and a production method thereof, belonging to the technical field of strip steel production. Background Art

[0002] Steel strapping is widely used in the packaging of steel, non-ferrous metals, building materials, papermaking, textiles and other products. To ensure the safety of loading and unloading and transportation, the strapping is required to have high strength and good plasticity. At present, many patents involve the production methods of high-strength strapping steel. According to the difference in its strengthening method, the production process of strapping steel can be divided into three types, namely lead bath isothermal quenching combined with tempering process, two-phase zone quenching combined with tempering process, and cold rolling combined with bluing process.

[0003] The lead bath isothermal quenching combined with tempering process, that is, the use of a lead bath furnace for heat treatment, is mainly used for the production of strapping with a tensile strength of 980MPa or above. For example, patent CN104264048B uses a lead bath isothermal quenching + tempering process to achieve the production of 1500MPa high-strength strapping. However, the lead vapor produced during the lead bath process will cause environmental pollution and endanger human health. Countries are gradually restricting the commissioning of lead bath furnaces. The two-phase zone quenching + tempering process is a heat treatment method that has received considerable attention in recent years. It uses water quenching instead of lead bath quenching. For example, patent CN101805870B discloses a high-strength strapping steel with a tensile strength higher than 1100MPa and its manufacturing method. The invention uses a two-phase zone quenching + tempering process. The structure obtained by the two-phase zone quenching + tempering process is a carbide + tempered martensite structure, and its elongation is limited, and the quenching treatment has the problem of difficult plate shape control.

[0004] Compared with the lead bath isothermal quenching combined with tempering process and the two-phase zone quenching combined with tempering process, the cold rolling combined with bluing process has a simple process flow, high production efficiency, and no need to reheat to austenitization, saving energy consumption. Therefore, it is the most commonly used process in the current strapping production. The strapping produced by the cold rolling combined with bluing process mainly obtains high strength through cold rolling work hardening, and then uses subsequent bluing treatment to improve the elongation of steel. For example, the strapping steel described in patents CN114645187A and CN103352165B is produced in this way. This method is mostly used for the production of strapping steel with a tensile strength of 950MPa and below. In recent years, in order to improve the strength of strapping steel, some researchers have adopted medium-temperature coiling to obtain a hot-rolled substrate with a bainite structure as the main structure, and then combined with a cold rolling large reduction strategy to achieve the production of 980-1100MPa high-strength strapping steel, such as patents CN109440010B and CN106282818B. Although this solution can improve the strength of the strapping steel, the substrate is strengthened by bainite and the cold rolling adopts a large reduction strategy, which will lead to poor elongation of the strapping steel. In order to improve the elongation of steel, patent CN106282818B also increases the annealing temperature and prolongs the annealing time, but the annealing is completed in a vertical annealing furnace, and the temperature and time of conventional bluing equipment are difficult to meet the process requirements.

[0005] Therefore, in view of the current status of cold rolling combined with bluing process, it is necessary to provide a new production process to achieve the optimization and improvement of the tensile strength and elongation of high-strength strapping. Summary of the invention

[0006] The present invention provides a high-strength strapping steel and a production method thereof, which solves the problem that it is difficult to produce high-strength and high-elongation strapping steel under the conditions of cold rolling combined with bluing process.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A high-strength strapping steel, produced by cold rolling combined with bluing process, the obtained strapping steel has a tensile strength R m ≥1000MPa, elongation A 30 ≥12%;

[0009] The production method of the high-strength strap steel specifically comprises the following steps:

[0010] Step S1: steelmaking process, the converter molten steel is subjected to RH treatment after LF refining, and calcium treatment is performed at the same time, and cast into continuous casting billets, and the mass percentage of Cr in the refined molten steel is controlled to be 0.5-0.9%, and the mass percentage of Ca is 0.0010-0.0040%;

[0011] Step S2: In the continuous casting process, electromagnetic stirring is used at the end of the secondary cooling zone, the electromagnetic stirring current is set to 300-400A, and the frequency is set to 5-7Hz; dynamic soft reduction technology is used in the fan-shaped section, and when the solid phase ratio is between 0.30-0.70, the total reduction amplitude is 3-4mm, and the reduction rate is 0.8-1.2mm / m;

[0012] Step S3: Heating and rolling process, the continuous casting billet is heated to obtain a high-temperature slab, the soaking temperature range of the heating section is 1200-1230°C, the heating time is 120-170min, and the final rolling temperature setting range is 860-890°C;

[0013] Step S4: laminar cooling and coiling process, during the laminar cooling process, air cooling is adopted in the front section and water spray cooling is adopted in the rear section, and the coiling target temperature is set to 620-640°C when the cooled slab is coiled into a coil, so as to produce a hot-rolled steel plate;

[0014] Step S5: cold rolling process, the cold rolling process is carried out in 5 passes, the total reduction rate is set to 60-70%, and the reduction rate of the last pass is set to 5-10%, at this time, the hot-rolled steel sheet is made into a cold-rolled strip;

[0015] Step S6: bluing process, using electric induction heating to treat the steel material so that its surface presents a bluing effect, during the heating process, the heating temperature is set to 500-550°C, the bluing time is set to 30-50s, and high-temperature steam is used as the bluing medium;

[0016] Step S7: cooling process;

[0017] Step S8: painting, drying and waxing process;

[0018] Step S9: coiling process to produce finished bundled steel strips;

[0019] Furthermore, in step S1, when performing RH treatment, the RH vacuum degree is set to ≤ 2 mBa, the degassing time is 10-20 min, the net circulation time is 5-15 min, and the soft stirring time after calcium treatment is 10-15 min;

[0020] Furthermore, in step S1, the chemical composition of the cast continuous casting billet includes, by mass percentage, C: 0.26-0.32%, Si: 0.10-0.20%, Mn: 0.6-0.9%, P≤0.016%, Cr: 0.5-0.9%, S≤0.006%, Ca: 0.0010-0.0030%, Al: 0.01-0.05%, and the rest is iron and unavoidable impurities;

[0021] Further, in step S4, the hot-rolled steel plate produced through the laminar cooling and coiling process has a thickness of 2.3-3.0 mm, a tensile strength of 650-780 MPa, an elongation A ≥ 30%, a structure mainly composed of ferrite combined with pearlite, ferrite accounting for 30-40%, and the rest being pearlite, and a ferrite grain size of 7-9;

[0022] Furthermore, in step S5, the cold-rolled steel strip produced through the cold rolling process has a thickness of 0.69-1.35 mm;

[0023] Furthermore, in step S6, after annealing through the bluing process, the number of consecutive 90° bends can be ≥12 times.

[0024] Through the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The production method of high-strength strap steel provided by the present invention adopts electromagnetic stirring in the secondary cooling zone and dynamic soft pressure in the fan-shaped zone in the continuous casting process to eliminate the influence of uneven composition and structure on the plasticity of the steel;

[0026] 2. The production method of the high-strength strapping steel provided by the present invention obtains an appropriate organizational state by coordinating the cooling mode and the coiling temperature during the cooling and coiling process, and then obtains high-strength and high-elongation hot-rolled strapping steel, which provides a guarantee for the plasticity of the subsequent high-strength strapping;

[0027] 3. The production method of the high-strength strapping steel provided by the present invention, in the cold rolling process, based on the comprehensive influence of the cold rolling deformation rate on the strength and plasticity of the steel, reasonably controls the cold rolling process reduction rate, cooperates with the blueing treatment of the strapping steel, and obtains high-strength strapping steel with high compressive strength and high elongation;

[0028] 4. The production method of high-strength strapping steel provided by the present invention takes measures in sequence in key processes such as steelmaking and continuous casting, hot rolling, laminar cooling, cold rolling, and bluing treatment, focusing on improving the quality of the core of the substrate, optimizing the organizational state of the substrate, and reasonably setting the cold rolling and bluing processes, thereby achieving comprehensive regulation of the strength and plasticity of the high-strength strapping. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0030] Figure 1 The present invention provides a flow chart of the production method of high-strength strapping steel. DETAILED DESCRIPTION

[0031] The specific dimensions used in this embodiment are only for illustrating the technical solution and do not limit the protection scope of the present invention.

[0032] As described in the background technology, the cold rolling + bluing process is the most commonly used process by strapping manufacturers. Cold rolling obtains high strength, and bluing improves elongation. It has the advantages of simple equipment and fast production rhythm. However, the existing technology of cold rolling + bluing cannot simultaneously meet the effects of high strength and high elongation. Therefore, the present application provides a production method for high-strength strapping steel to improve the strength and elongation of strapping steel after cold rolling and bluing.

[0033] The purpose of this production method is to produce a high-strength strapping steel with a tensile strength R m ≥1000MPa, elongation A 30 ≥12%, the tensile strength of this strapping steel is at least 1000MPa, which is much higher than the strength requirement of 550-850MPa for normal strapping steel. This application achieves comprehensive regulation of the strength and plasticity of high-strength strapping by taking measures in key processes such as steelmaking and continuous casting, hot rolling, laminar cooling, cold rolling, and bluing treatment, focusing on improving the quality of the core of the substrate, optimizing the substrate structure, and reasonably setting the cold rolling and bluing processes.

[0034] Figure 1 As shown, the specific steps include:

[0035] Step S1: Steelmaking process, the converter molten steel is subjected to RH treatment after LF refining. The steelmaking process is produced in the LF+RH mode and calcium treatment is performed. It should be noted that degassing, net circulation and soft stirring time after calcium treatment should be guaranteed to reduce the influence of inclusions and gas elements on the plasticity of steel.

[0036] Regarding the influence of elements on strapping steel, the main ones are Cr and Ca. The effect of the alloying element Cr is mainly reflected in the following three aspects: First, the combined effect of Cr and Mn can significantly improve the strength and tempering resistance of steel. Cr is mainly enriched in cementite, with less ferrite content, and the effect of improving tensile strength is more obvious. Cr can also delay the decomposition of cementite in steel alloys, so that it has a certain resistance to tempering softening and avoids the bluing process that causes a significant reduction in the strength of steel; secondly, Cr can delay the pearlite phase transformation process and refine the pearlite lamellar spacing, thereby improving the plasticity of steel, thereby ensuring a higher elongation; finally, Cr can also slow down the oxidation rate and avoid the formation of powdery or flaky oxide layers on the surface of the blue strap. For the alloying element Ca, it mainly improves the morphology of inclusions through calcium treatment to avoid the formation of long strip inclusions. Long strip inclusions such as MnS are distributed in linear or thin sheets after rolling deformation, thus affecting the elongation of the strapping steel. Therefore, the role of Ca is mainly to improve the morphology of inclusions and avoid a significant decrease in the elongation of steel caused by cold rolling deformation of inclusions.

[0037] Therefore, in this step, considering the strength and elongation requirements of the subsequent steel grades after cold rolling and blueing, the mass percentage of Cr in the refined molten steel is controlled to be 0.5-0.9%, and the mass percentage of Ca is controlled to be 0.0010-0.0040%.

[0038] Regarding the influence of inclusions on strapping steel, inclusions, especially Class A inclusions, are distributed in flake or linear form after subsequent cold rolling deformation, which breaks the continuity of the matrix and affects the shaping of the steel. Therefore, the main purpose of RH is to reduce the source of inclusions, thereby reducing the influence of inclusions on elongation.

[0039] Regarding degassing, net circulation and soft stirring time after calcium treatment, preferably, when performing RH treatment, the RH vacuum degree is set to ≤2mBa, the degassing time is 10-20min, the net circulation time is 5-15min, and the soft stirring time after calcium treatment is 10-15min.

[0040] The chemical composition of the finally cast continuous casting billet includes, by mass percentage, C: 0.26-0.32%, Si: 0.10-0.20%, Mn: 0.6-0.9%, P≤0.016%, Cr: 0.5-0.9%, S≤0.006%, Ca: 0.0010-0.0030%, Al: 0.01-0.05%, and the rest is iron and unavoidable impurities.

[0041] Step S2: Continuous casting process. In this step, continuous casting is significantly optimized by using electromagnetic stirring at the end of the second cooling zone and dynamic soft reduction technology in the fan-shaped section. Since segregation will cause uneven performance of components at different positions, such as large segregation in the core and poor uniformity of the core structure, the elongation after cold rolling will not meet the requirements. The electromagnetic stirring at the end of the second cooling zone breaks the dendrites by applying a certain frequency of current to the liquid core of the billet, forming equiaxed crystals in the core, reducing the image of banded structure and improving the uniformity of the structure; preferably, the electromagnetic stirring current is set to 300-400A and the frequency is set to 5-7Hz. The light reduction technology is to implement roll gap reduction at a certain position when the ingot is cooled, and to apply pressure at the end of solidification to prevent the lateral flow of molten steel enriched with solute elements between crystals, reduce or eliminate center segregation, and compensate for solidification shrinkage to make the ingot denser; preferably, when the solid phase ratio is between 0.30-0.70, the total reduction amplitude is 3-4mm, the reduction rate is 0.8-1.2mm / m, and the continuous casting ingot is cast.

[0042] In this step, electromagnetic stirring at the end of the secondary cooling zone and dynamic soft pressing technology in the fan-shaped section are used to eliminate the influence of abnormal core components and structures on the plasticity of high-strength strapping steel, improve the core component and structure uniformity of the slab, and cooperate with the RH process to ensure that the steel plate has good plasticity.

[0043] Step S3: Heating and rolling process, the continuous casting billet is heated to obtain a high-temperature slab, the soaking temperature range of the heating section is 1200-1230°C, the heating time is 120-170min, and the final rolling temperature setting range is 860-890°C.

[0044] Step S4: laminar cooling and coiling process, through the coordination of cooling mode and coiling temperature, a certain organizational state is obtained to improve the plasticity of the steel plate. In the laminar cooling process, air cooling is used in the front stage, so that the "soft phase" ferrite can be fully precipitated, and water spray cooling is used in the back stage, so that the "hard phase" pearlite transformation occurs in the coiling stage, thereby obtaining a small and uniform interlamellar spacing. Preferably, the coiling target temperature is set to 620-640℃ when the cooled slab is coiled into a coil.

[0045] The hot-rolled steel plate made through laminar cooling and coiling process has a thickness of 2.3-3.0mm, a tensile strength of 650-780MPa, an elongation A≥30%, and a structure mainly composed of ferrite combined with pearlite, with ferrite accounting for 30-40% and the rest being pearlite. The ferrite grain size is 7-9.

[0046] Step S5: Cold rolling process. Cold rolling can reduce the thickness of the steel plate and improve the thickness accuracy of the steel plate. Cold rolling deformation will cause work hardening of the steel plate, which will increase the strength of the steel plate on the one hand and reduce the plasticity of the steel plate on the other hand. In order to meet the strength and plasticity requirements of the finished high-strength strapping steel, it is necessary to reasonably select the cold rolling reduction rate based on the performance and organizational characteristics of the hot-rolled steel plate and the work hardening characteristics of the steel plate. If the reduction rate is too small, the strength of the steel plate will be limited after cold rolling and blueing, and it is difficult to meet the strength requirements of the strapping steel; if the reduction rate is too large, the plasticity of the cold-rolled steel plate will decrease too much, and it will be difficult to meet the elongation requirements of the strapping after blueing annealing.

[0047] Preferably, the cold rolling process is carried out in 5 passes, the total reduction rate is set to 60-70%, and the reduction rate of the last pass is set to 5-10%, at which time the hot-rolled steel sheet is made into a cold-rolled strip.

[0048] Step S6: bluing process. The role of bluing treatment is mainly reflected in two aspects. First, an oxide layer of a certain thickness and phase composition can be obtained to improve the corrosion resistance of the strap; second, the bluing process will reduce the stress of the cold-rolled steel sheet and play a role in tempering. The bluing process heating temperature and bluing time process of the present invention are given by comprehensively considering the surface quality and the performance of the strap. If the heating temperature is too high and the insulation time is too long, the oxide layer on the surface of the strap will peel and powder off; if the temperature is too low and the insulation time is too short, the elongation of the steel plate after bluing is difficult to meet the requirements.

[0049] The bluing process provided in the present application uses electric induction heating to treat the steel so that its surface presents a bluing effect. During the heating process, the heating temperature is set to 500-550°C, the bluing time is set to 30-50s, and high-temperature steam is used as the bluing medium.

[0050] The above step S4 obtains an appropriate organizational state by coordinating the cooling mode and the coiling temperature to obtain a high-strength and high-elongation hot-rolled strapping steel. Based on the comprehensive influence of the cold rolling deformation rate on the strength and plasticity of the steel in step S5, the cold rolling process reduction rate is reasonably controlled to obtain a cold-rolled steel plate with a thickness of 0.69-1.35 mm, and the strapping steel is bluing treated in step S6; followed by a cooling process in step S7, a painting, drying and waxing process in step S8, and a coiling process in step S9 to obtain a tensile strength R m ≥1000MPa, elongation A 30 ≥12%, high-strength strapping steel with continuous 90° bending times ≥12 times.

[0051] Finally, this application is based on the cold rolling + bluing treatment process. By taking measures in the key processes such as steelmaking continuous casting, hot rolling, laminar cooling and coiling, cold rolling, bluing treatment, etc., a high-strength strapping steel with high strength and high elongation in the C-Si-Mn-Cr-Ca component system is obtained. Compared with the lead bath quenching and dual-phase zone heat treatment process of traditional high-strength strapping steel, the adopted process is simple, the production rhythm is fast and it is environmentally friendly.

[0052] Next, in order to verify the superiority of the production method of high-strength strapping steel, this application also provides 3 groups of specific cases, combined with 7 groups of comparative examples, to intuitively compare the tensile strength, elongation, repeated 90-degree bending times and surface quality of the strapping steels produced by various production methods. Example

[0053] Embodiment 1:

[0054] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0055] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0056] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 350A and the frequency is set to 6Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3.5mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0057] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0058] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0059] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 68%, and the reduction rate of the last pass is set to 7%.

[0060] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 530°C, the bluing time is 45s, and the bluing medium is high-temperature steam.

[0061] Step 7. Cool down.

[0062] Step 8: Paint, dry and wax.

[0063] Step 9: Collect the paper.

[0064] The final tensile strength of the strapping steel is R m is 1025MPa, elongation A 30 It is 14.0%, and the number of repeated 90-degree bending is 14 times. It is blue-black and the surface oxide layer does not fall off.

[0065] Embodiment 2:

[0066] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled on four stands to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished straps. The specific process steps are as follows:

[0067] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.5% and the mass fraction of Ca to be 0.0010% after the refining.

[0068] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 300A and the frequency is set to 5Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3~4mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 0.8mm / m.

[0069] The third step is heating and rolling. The average heating temperature in the heating section is 1200~1220℃, the heating time is 120~140min, and the final rolling temperature is set at 880~890℃.

[0070] The fourth step is laminar cooling and coiling. The laminar flow adopts air cooling at the front and water spray cooling at the rear. The coiling target temperature is set to 640℃.

[0071] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 60%, and the reduction rate of the last pass is set to 5%.

[0072] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 550°C, the bluing time is 50s, and the bluing medium is high-temperature steam.

[0073] Step 7. Cool down.

[0074] Step 8: Paint, dry and wax.

[0075] Step 9: Collect the paper.

[0076] The final tensile strength of the strapping steel is R m 1030MPa, elongation A 30 It is 13.5%, and the number of repeated 90-degree bending is 13 times. It is blue-black and the surface oxide layer does not fall off.

[0077] Embodiment 3:

[0078] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0079] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.9% and the mass fraction of Ca to be 0.0022% after the refining.

[0080] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 400A and the frequency is set to 7Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 4mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0081] The third step is heating and rolling; the average heating temperature in the heating section is 1200~1220℃, the heating time is 120~140min, and the final rolling temperature is set at 880~890℃.

[0082] The fourth step is laminar cooling and coiling. The laminar flow adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 620℃.

[0083] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 70%, and the reduction rate of the last pass is set to 10%.

[0084] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 500°C, the bluing time is 30s, and the bluing medium is high-temperature steam.

[0085] Step 7. Cool down.

[0086] Step 8: Paint and wax.

[0087] Step 9: Roll up the strapping.

[0088] The final tensile strength of the strapping steel is R m 1040MPa, elongation A 30 It is 14.2%, and the number of repeated 90-degree bending is 15 times. It is blue-black and the surface oxide layer does not fall off.

[0089] Comparative Example 1:

[0090] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0091] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.20% and the mass fraction of Ca to be 0.0010% after the refining.

[0092] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 350A and the frequency is set to 6Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3.5mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0093] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0094] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0095] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 68%, and the reduction rate of the last pass is set to 7%.

[0096] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 530°C, the bluing time is 45s, and the bluing medium is high-temperature steam.

[0097] Step 7. Cool down.

[0098] Step 8: Paint, dry and wax.

[0099] Step 9: Collect the paper.

[0100] The final tensile strength of the strapping steel is R m 980MPa, elongation A 30 It is 9.8%, and the number of repeated 90-degree bending times is 11. It is blue-black and the surface oxide layer is slightly peeled off.

[0101] Comparative Example 2:

[0102] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0103] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0104] The second step is continuous casting.

[0105] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0106] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0107] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 68%, and the reduction rate of the last pass is set to 7%.

[0108] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 530°C, the bluing time is 45s, and the bluing medium is high-temperature steam.

[0109] Step 7. Cool down.

[0110] Step 8: Paint, dry and wax.

[0111] Step 9: Collect the paper.

[0112] The final tensile strength of the strapping steel is R m is 1020MPa, elongation A 30 It is 9.5%, and the number of repeated 90-degree bending is 9 times. It is blue-black and the surface oxide layer does not fall off.

[0113] Comparative Example 3:

[0114] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0115] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0116] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 200A and the frequency is set to 3Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 2.0mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 0.7mm / m.

[0117] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0118] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0119] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 68%, and the reduction rate of the last pass is set to 7%.

[0120] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 530°C, the bluing time is 45s, and the bluing medium is high-temperature steam.

[0121] Step 7. Cool down.

[0122] Step 8: Paint, dry and wax.

[0123] Step 9: Collect the paper.

[0124] The final tensile strength of the strapping steel is R m is 1010MPa, elongation A 30 The surface oxide layer is 10.0%, and the number of repeated 90-degree bending is 10 times. It is blue-black and there is no shedding of the surface oxide layer.

[0125] Comparative Example 4:

[0126] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0127] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0128] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 350A and the frequency is set to 6Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3.5mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0129] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0130] The fourth step is laminar cooling and coiling. The laminar cooling adopts the conventional front-stage main cooling mode, and the coiling target temperature is set to 570℃.

[0131] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 68%, and the reduction rate of the last pass is set to 7%.

[0132] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 530°C, the bluing time is 45s, and the bluing medium is high-temperature steam.

[0133] Step 7. Cool down.

[0134] Step 8: Paint, dry and wax.

[0135] Step 9: Collect the paper.

[0136] The final tensile strength of the strapping steel is Rm 1022MPa, elongation A 30 It is 10.5%, and the number of repeated 90-degree bending is 9 times. It is blue-black and the surface oxide layer does not fall off.

[0137] Comparative Example 5:

[0138] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0139] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0140] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 350A and the frequency is set to 6Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3.5mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0141] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0142] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0143] In the fifth step, cold rolling is carried out in 4 passes, the total reduction rate is set to 45%, and the reduction rate of the last pass is set to 3%.

[0144] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 530°C, the bluing time is 45s, and the bluing medium is high-temperature steam.

[0145] Step 7. Cool down.

[0146] Step 8: Paint, dry and wax.

[0147] Step 9: Collect the paper.

[0148] The final tensile strength of the strapping steel is R m 975MPa, elongation A 30 It is 12.0%, and the number of repeated 90-degree bending is 11 times. It is blue-black and the surface oxide layer does not fall off.

[0149] Comparative Example 6:

[0150] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0151] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0152] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 350A and the frequency is set to 6Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3.5mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0153] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0154] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0155] In the fifth step, cold rolling is carried out in 4 passes, the total reduction rate is set to 78%, and the reduction rate of the last pass is set to 12%.

[0156] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 530°C, the bluing time is 45s, and the bluing medium is high-temperature steam.

[0157] Step 7. Cool down.

[0158] Step 8: Paint, dry and wax.

[0159] Step 9: Collect the paper.

[0160] The final tensile strength of the strapping steel is R m 1032MPa, elongation A 30 It is 7.0%, and the number of repeated 90-degree bending is 8 times. It is blue-black and the surface oxide layer does not fall off.

[0161] Comparative Example 7:

[0162] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0163] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0164] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 350A and the frequency is set to 6Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3.5mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0165] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0166] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0167] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 68%, and the reduction rate of the last pass is set to 7%.

[0168] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 450°C, the bluing time is 20s, and the bluing medium is high-temperature steam.

[0169] Step 7. Cool down.

[0170] Step 8: Paint, dry and wax.

[0171] Step 9: Collect the paper.

[0172] The final tensile strength of the strapping steel is R m 1035MPa, elongation A 30 It is 13.0%, the number of repeated 90-degree bending is 11 times, it is light blue, and the surface is powdery and falls off.

[0173] Comparative Example 8:

[0174] The molten steel in the converter is refined by LF and treated by RH, and then cast into continuous casting billets. The continuous casting billets are heated to obtain high-temperature slabs, which are then rolled, cooled, and coiled to form hot-rolled steel plates. The hot-rolled steel plates are stripped, pickled, and cold-rolled to form cold-rolled strips. The cold-rolled strips are stripped, bluing, cooled, painted, dried, waxed, and coiled in the strapping unit to form finished strapping. The specific process steps are as follows:

[0175] The first step is steelmaking. After the LF refining of the converter steel is completed, RH treatment is carried out to control the mass percentage of Cr element in the steel to be 0.70% and the mass fraction of Ca to be 0.0030% after the refining.

[0176] The second step is continuous casting. Electromagnetic stirring is used at the end of the second cooling zone. The electromagnetic stirring current is set to 350A and the frequency is set to 6Hz. Dynamic soft reduction is used in the fan-shaped section. The total reduction is 3.5mm between the solid phase ratio of 0.30~0.70 and the reduction rate is 1.0mm / m.

[0177] The third step is heating and rolling; the average heating temperature in the heating section is 1210~1200℃, the heating time is 140~160min, and the final rolling temperature is set at 870~880℃.

[0178] The fourth step is laminar cooling and coiling. The laminar cooling adopts air cooling in the front section and water spray cooling in the back section. The coiling target temperature is set to 630℃.

[0179] In the fifth step, cold rolling is carried out in 5 passes, the total reduction rate is set to 68%, and the reduction rate of the last pass is set to 7%.

[0180] The sixth step is to use electric induction heating for bluing. The heating temperature is set to 600°C, the bluing time is 55s, and the bluing medium is high-temperature steam.

[0181] Step 7. Cool down.

[0182] Step 8: Paint, dry and wax.

[0183] Step 9: Collect the paper.

[0184] The final tensile strength of the strapping steel is R m 972MPa, elongation A 30 It is 12.5%, and the number of repeated 90-degree bending is 11 times. It is black and the surface is powdery and falls off.

[0185] The above examples are compared with the comparative examples to form Table 1:

[0186] Table 1 Tensile properties and surface quality of strapping in the embodiments of the present invention and the comparative examples

[0187]

[0188] It can be seen from Table 1 above that the strapping steel obtained by the production method of high-strength strapping steel provided in this application can achieve the following tensile strength R m ≥1000MPa, elongation A 30 ≥12%, repeated 90 degree bending times ≥12 times.

[0189] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art to which this application belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0190] The meaning of "and / or" described in this application means that the situations where each exists alone or both exist at the same time are included.

[0191] The term “connection” as used in this application may mean a direct connection between components or an indirect connection between components via other components.

[0192] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for producing high-strength strapping steel, characterized in that: The specific steps include: Step S1: steelmaking process, the converter molten steel is subjected to RH treatment after LF refining, and calcium treatment is performed at the same time, and cast into continuous casting billets, and the mass percentage of Cr in the refined molten steel is controlled to be 0.5-0.9%, and the mass percentage of Ca is 0.0010-0.0040%; The chemical composition of the cast continuous casting billet includes, by mass percentage, C: 0.26-0.32%, Si: 0.10-0.20%, Mn: 0.6-0.9%, P≤0.016%, Cr: 0.5-0.9%, S≤0.006%, Ca: 0.0010-0.0030%, Al: 0.01-0.05%, and the rest is iron and unavoidable impurities; Step S2: In the continuous casting process, electromagnetic stirring is used at the end of the secondary cooling zone, the electromagnetic stirring current is set to 300-400A, and the frequency is set to 5-7Hz; dynamic soft reduction technology is used in the fan-shaped section, and when the solid phase ratio is between 0.30-0.70, the total reduction amplitude is 3-4mm, and the reduction rate is 0.8-1.2mm / m; Step S3: Heating and rolling process, the continuous casting billet is heated to obtain a high-temperature slab, the soaking temperature range of the heating section is 1200-1230°C, the heating time is 120-170min, and the final rolling temperature setting range is 860-890°C; Step S4: laminar cooling and coiling process, during the laminar cooling process, air cooling is adopted in the front section and water spray cooling is adopted in the rear section, and the coiling target temperature is set to 620-640°C when the cooled slab is coiled into a coil, so as to produce a hot-rolled steel plate; The hot-rolled steel plate made through laminar cooling and coiling process has a thickness of 2.3-3.0mm, a tensile strength of 650-780MPa, an elongation A≥30%, and a structure mainly composed of ferrite combined with pearlite, with ferrite accounting for 30-40% and the rest being pearlite, and a ferrite grain size of 7-9; Step S5: cold rolling process, the cold rolling process is carried out in 5 passes, the total reduction rate is set to 60-70%, and the reduction rate of the last pass is set to 5-10%, at this time, the hot-rolled steel sheet is made into a cold-rolled strip; Step S6: bluing process, using electric induction heating to treat the steel material so that its surface presents a bluing effect, during the heating process, the heating temperature is set to 500-550°C, the bluing time is set to 30-50s, and high-temperature steam is used as the bluing medium; Step S7: cooling process; Step S8: painting, drying and waxing process; Step S9: Coiling process to produce finished bundled steel strips.

2. The method for producing high-strength strapping steel according to claim 1, characterized in that: In step S1, when performing RH treatment, the RH vacuum degree is set to ≤ 2 mBa, the degassing time is 10-20 min, the net circulation time is 5-15 min, and the soft stirring time after calcium treatment is 10-15 min.

3. The method for producing high-strength strapping steel according to claim 1, characterized in that: In step S5, the cold-rolled steel strip produced through the cold rolling process has a thickness of 0.69-1.35 mm.

4. The high-strength strapping steel obtained by the production method according to claim 1 is characterized in that: Tensile strength R m ≥1000MPa, elongation A 30 ≥12%. After annealing in the bluing process, it can achieve continuous 90° bending times ≥12 times.

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